Last time, we discussed DRS, a defensive metric that assigns run values to defensive plays and gives players credit based on how valuable each play they made was. This week, we're discussing UZR, a defensive metric that assigns run values to defensive plays and gives players credit based on how valuable each play they made was.

The overlap of UZR/DRS

Both UZR and DRS work principally by determining the probability that a play is made on a batted ball, assigning a run value to a batted ball and giving a player credit or penalizing a player for making or missing a play, respectively.

For example, if a batted ball is caught 25 percent of the time, and that batted ball is worth 0.6 runs on average, then a defender who makes the play receives 0.6 times (1 - .25) = +.45 runs worth, and if he misses it, then he is penalized -.15 runs.

Both UZR and DRS use the same dataset, Baseball Info Solution's batted ball data. BIS classifies balls based on their quality of contact, spray, elevation and type.

Both UZR and DRS also give run credit for different aspects of play, like giving outfielders credit for throwing the ball in to throw out runners or keep runners from advancing, or for turning double plays.

Think UZR and DRS as toddlers playing with Legos to build a helicopter: they both use the same materials and are attempting to accomplish the same goal, but they're taking different paths to do so.

Different strokes for different folks

So why, then, do UZR and DRS disagree so much for these guys?

Player

DRS (2017)

UZR (2017)

Kyle Seager

-2

6.2

Miguel Cabrera

-8

3.3

Justin Turner

6

-1.1

UZR grades Seager and Cabrera as above-average defenders in 2017, and Turner as well below average, but DRS says the opposite. Clearly, there's a big disagreement here.

There are several factors attributing to the disagreement, but perhaps s the biggest difference is that UZR uses larger "buckets" than DRS.

DRS and UZR perform their calculations by grouping batted balls into "buckets" - similar types of batted balls grouped together. UZR's buckets are larger, so on the back end, they're less precise than DRS, but as Mitchel Lichtman, who performs UZR calculations for FanGraphs, describes , DRS's data from BIS is not necessarily precise enough to warrant the size of the buckets that DRS uses, so there's a trade-off with both metrics.

So in that respect, it's possible that a batted ball is measured by DRS to be much more valuable than measured by UZR, and thus, a player receives less credit from UZR than they might from DRS.

In the long term, these differences even out quite a bit. Here are those same three players as before, but this time I've displayed their DRS and UZR values over the past three years.

Player

DRS (2015-2017)

UZR (2015-2017)

Kyle Seager

14

12.4

Miguel Cabrera

-10

6.5

Justin Turner

18

16.1

The values for Seager and Turner are much more in concert with each other in regard to DRS and UZR, though Cabrera paints a polarizing picture defensively.

Cabrera's differences could be explained by the fact that DRS calculates the penalties and credits for batted balls that multiple fielders can make a play on differently from UZR.

If a ball can be fielded by either of two players and both miss, DRS punishes those players each more than UZR. If either succeeds, that player receives more credit with DRS than they would with UZR. Because of these and other factors, DRS tends to assign a greater spread of values than UZR. Among qualified players, the best and worst player in 2017 by DRS differed by 59 DRS, but that figure was only 33.8 for UZR.

Cabrera has spent much of the past three seasons sharing the right half of the infield with Ian Kinsler, who has consistently graded out as a stellar defensive second baseman (37 DRS, 20.9 UZR from 2015-2017). Cabrera, with very limited range, might opt to cover the bag and let Kinsler dive after balls in both directions. If Kinsler can't make the play, both are punished more by DRS than UZR, but Kinsler has a better ability to make plays than Cabrera, so he can make up for his shortcomings with those plays.

Cabrera can't, as an aging first baseman with limited range, so DRS punishes him more than UZR. It's not the only reason for UZR and DRS's differences, but it's certainly a factor.

All in how it's used

The reason that DRS and UZR function separately lies in the small differences between the two: some sabermetricians prefer the small differences of UZR to the differences of DRS, or vice versa. It's not an objective measurement, where one metric is strictly better than the other, but a matter of preference.

UZR and DRS also exist partially to support their respective forms of WAR: UZR is used in calculating fWAR for FanGraphs, whereas DRS is used in calculating rWAR for Baseball Reference. Like calling a carbonated beverage "soda" in one region or "pop" in another.

Or pronouncing ".gif" with a hard G sound or pronouncing it correctly, it's just different strokes for different folks.